Magnetic disk drive with adjustment of rotational balance

Abstract

Embodiments of the invention provide, in a compact magnetic disk drive, a stable structure capable of reducing self-oscillation occurring from disk spinning, while suppressing generation of dust and dirt. In one embodiment, a magnetic disk is mounted on a hub of a spindle motor. A clamp is further attached to secure the magnetic disk in position. A plurality of opening portions are formed in the clamp around an axis. A counterweight formed of an elastic material is mounted in the opening portion by being press-fitted therein. The counterweight is less likely to generate dust and dirt through friction during insertion and looseness. A gap is provided between the clamp and the hub at locations near the opening portions. The counterweight has a protruded portion on a side surface of a circular column portion. The protruded portion slides into the gap between the clamp and the hub, counteracting a tendency of the counterweight to drop out of position.

1. A magnetic disk drive, comprising:
 a motor hub; 
 a clamp board serving as a sheet member mounted on the motor hub and having opening portions passing through the sheet member formed on each of a plurality of directional lines as viewed from a disk rotary axis; 
 a magnetic disk clamped by the motor hub and the clamp board; and 
 a counterweight formed of an elastic material and mounted by being disposed into at least one of the plurality of opening portions; 
 wherein the motor hub has a recessed portion formed at a position opposing the opening portion in the clamp board; 
 wherein the clamp board is disposed by having a gap provided from the motor hub at a location near at least each of the plurality of opening portions; and 
 wherein the counterweight includes a protruded portion on a side surface thereof, the protruded portion being engaged with the gap when mounted in the opening portion; 
 wherein the counter weight includes an upper portion and a lower portion that are symmetrical and formed on opposite sides of the protruded portion, 
 wherein the lower portion of the counter weight corresponds to the depth of the recessed portion of the motor hub. 
 
     
     
       2. The magnetic disk drive according to  claim 1 ,
 wherein the counterweight is mounted in a disk assembly including the magnetic disk secured to the motor hub using the clamp board and a mounting position of the counterweight is selected from among the plurality of opening portions according to a rotational balance of the disk assembly. 
 
     
     
       3. The magnetic disk drive according to  claim 1 ,
 wherein the opening portions are formed at predetermined spaced intervals on a circumference of a circle having the rotary axis as a center thereof. 
 
     
     
       4. The magnetic disk drive according to  claim 1 ,
 wherein the counterweight has an outline including a portion of a generally circular column shape combined with an annular protruded portion running along a circumference of a side surface of the circular column portion. 
 
     
     
       5. The magnetic disk drive according to  claim 4 ,
 wherein the counterweight includes an opening portion formed along an axis of the circular column portion. 
 
     
     
       6. The magnetic disk drive according to  claim 1 ,
 wherein the opening portion formed in the clamp board has an opening of a circular shape; and 
 the recessed portion having a circular opening of a size corresponding to the shape of the opening. 
 
     
     
       7. The magnetic disk drive according to  claim 6 ,
 wherein the counterweight has an outline including a portion of a generally circular column shape combined with an annular protruded portion running along a circumference of a side surface of the circular column portion, the annular protruded portion being located at a position a predetermined separating length away from each of upper and lower ends of the circular column portion. 
 
     
     
       8. The magnetic disk drive according to  claim 1 ,
 wherein the counterweight includes a filler material mixed with the elastic material, the filler material having a greater specific gravity than the elastic material. 
 
     
     
       9. The magnetic disk drive according to  claim 1 ,
 wherein the elastic material includes at least one of styrene-butadience rubber, butadiene rubber, butyl rubber, ethylene propylene rubber, nitrile rubber, chloroprene rubber, fluororubber, silicone rubber, urethane rubber, a styrene-based elastomer, an olefin-based elastomer, an urethane-based elastomer, and an ester-based elastomer. 
 
     
     
       10. A method of assembling a magnetic disk drive, the method comprising:
 providing a motor hub; 
 mounting a clamp board serving as a sheet member on the motor hub and having opening portions passing through the sheet member formed on each of a plurality of directional lines as viewed from a disk rotary axis; 
 clamping a magnetic disk by the motor hub and the clamp board; and 
 mounting a counterweight formed of an elastic material by being press-fitted into at least one of the plurality of opening portions; 
 wherein the motor hub has a recessed portion formed at a position opposing the opening portion in the clamp board; 
 wherein the clamp board is disposed by having a gap provided from the motor hub at a location near at least each of the plurality of opening portions; and 
 wherein the counterweight includes a protruded portion on a side surface thereof, the protruded portion being engaged with the gap when mounted in the opening portion; 
 wherein the counterweight includes an upper portion and a lower portion that are symmetrical and formed on opposite sides of the protruded portion; 
 wherein the lower portion of the counter weight corresponds to the depth of the recessed portion of the motor hub. 
 
     
     
       11. The method of assembling a magnetic disk drive according to  claim 10 ,
 wherein the counterweight is mounted in a disk assembly including the magnetic disk secured to the motor hub using the clamp board and a mounting position of the counterweight is selected from among the plurality of opening portions according to a rotational balance of the disk assembly. 
 
     
     
       12. The method of assembling a magnetic disk drive according to  claim 10 ,
 wherein the opening portions are formed at predetermined spaced intervals on a circumference of a circle having the rotary axis as a center thereof. 
 
     
     
       13. The method of assembling a magnetic disk drive according to  claim 10 ,
 wherein the counterweight has an outline including a portion of a generally circular column shape combined with an annular protruded portion running along a circumference of a side surface of the circular column portion. 
 
     
     
       14. The method of assembling a magnetic disk drive according to  claim 13 ,
 wherein the counterweight includes an opening portion formed along an axis of the circular column portion. 
 
     
     
       15. The method of assembling a magnetic disk drive according to  claim 10 ,
 wherein the opening portion formed in the clamp board has an opening of a circular shape; and 
 the recessed portion having a circular opening of a size corresponding to the shape of the opening. 
 
     
     
       16. The method of assembling a magnetic disk drive according to  claim 15 ,
 wherein the counterweight has an outline including a portion of a generally circular column shape combined with an annular protruded portion running along a circumference of a side surface of the circular column portion, the annular protruded portion being located at a position a predetermined separating length away from each of upper and lower ends of the circular column portion. 
 
     
     
       17. The method of assembling a magnetic disk drive according to  claim 10 ,
 wherein the counterweight includes a filler material mixed with the elastic material, the filler material having a greater specific gravity than the elastic material. 
 
     
     
       18. The method of assembling a magnetic disk drive according to  claim 10 ,
 wherein the elastic material includes at least one of styrene-butadience rubber, butadiene rubber, butyl rubber, ethylene propylene rubber, nitrile rubber, chloroprene rubber, fluororubber, silicone rubber, urethane rubber, a styrene-based elastomer, an olefin-based elastomer, an urethane-based elastomer, and an ester-based elastomer.